A bearing, as used herein, generally refers to the area where a first part of a machine supports another part which can move relative to the first part. An air bearing is a particular type of bearing in which a stream of pressurized air is forced through a gap between the two parts to maintain relatively frictionless support.
Air bearings are commonly used in coordinate measuring machines in order to provide essentially frictionless movement between parts, thus allowing high speed movement and accurate placement. Air bearings, however, require a large amount of pressurized air per unit time and thus have relatively high operating costs. Typically, an air compressor is run to supply a holding tank with enough air to keep the pressure in the tank between specified minimum and maximum levels. Air is released to the air bearing through a valve, a pressure regulator, and an outlet which leads from the tank to the bearing. The compressor is electrically feedback controlled to maintain the pressure in the holding tank within the specified pressure range, e.g., 10-12 atmospheres. Thus, when a pressure sensor indicates that the pressure in the tank is greater than 12 atmospheres, the compressor turns off; and when the pressure in the tank drops to below 10 atmospheres, the compressor turns on again. When the valve to the air bearing is open, the air which is being relieved from the tank to the air bearing must constantly be replenished by the compressor. Accordingly, when the air bearing is operating, the air compressor is on and operating most, if not all, of the time. Air compressors have relatively high energy consumption. Thus, maintaining the pressure in the air bearings of a machine is relatively costly.
Therefore, it is an object of the present invention to conserve air consumed by air bearings.
It is a further object of the present invention to provide an improved air bearing control system.
It is yet another object of the present invention to provide a coordinate measuring machine comprising air bearings having reduced operating costs.